I received a updated for my phone and the smart lock features disappeared.
I am using a Moto X4 and enjoyed the smart lock features that kept my phone unlocked at home and when my bluetooth watch was close by.
I have the My Choice + 1GB plan for my phone.

When I go to the security and settings menu, the smart lock menu option still exist, but it takes me to a blank screen that has no way for me to add devices or locations.

As the Android code fix/release cycles is managed by Google and the various phone manufactures, you may wish to reach out to Motorolo to see if they can provide any information.Motorola Product Support